U.S. patent number 7,746,595 [Application Number 12/240,254] was granted by the patent office on 2010-06-29 for disk drive comprising slanted line servo bursts having reverse polarity segments.
This patent grant is currently assigned to Western Digital Technologies, Inc.. Invention is credited to Guoxiao Guo, Jie Yu.
United States Patent |
7,746,595 |
Guo , et al. |
June 29, 2010 |
Disk drive comprising slanted line servo bursts having reverse
polarity segments
Abstract
A disk drive is disclosed comprising a disk having servo data
defining a plurality of servo tracks. The servo data comprises a
preamble, and a plurality of slanted line servo bursts recorded at
a tilt angle with respect to the preamble. At least one of the
slanted line servo bursts comprises a first polarity along a first
segment of the slanted line and a second polarity along a second
segment of the slanted line. A position error signal (PES) is
generated in response to a phase difference when reading the
preamble and the slanted line servo bursts.
Inventors: |
Guo; Guoxiao (Foothill Ranch,
CA), Yu; Jie (Irvine, CA) |
Assignee: |
Western Digital Technologies,
Inc. (Lake Forest, CA)
|
Family
ID: |
42271226 |
Appl.
No.: |
12/240,254 |
Filed: |
September 29, 2008 |
Current U.S.
Class: |
360/77.08 |
Current CPC
Class: |
G11B
5/59688 (20130101); G11B 5/59655 (20130101) |
Current International
Class: |
G11B
5/596 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Che et al, "Study of Lithographically Defined Data Track and Servo
Patterns", IEEE Transactions on Magnetics, vol. 43, No. 12, Dec.
2007, pp. 4106-4112. cited by other .
Office Action dated Oct. 26, 2009 from U.S. Appl. No. 12/240,374,
11 pages. cited by other .
Notice of Allowance dated Feb. 25, 2010 from U.S. Appl. No.
12/240,374, 7 pages. cited by other.
|
Primary Examiner: Wong; K.
Claims
What is claimed is:
1. A disk drive comprising: a disk comprising servo data defining a
plurality of servo tracks, wherein the servo data comprises: a
preamble; and a plurality of slanted line servo bursts recorded at
a tilt angle with respect to the preamble, wherein at least one of
the slanted line servo bursts comprises a first magnetic polarity
along a first segment of the slanted line and a second magnetic
polarity along a second segment of the slanted line; a head
actuated radially over the disk for generating a read signal; and
control circuitry operable to: generate a preamble read signal when
the head passes over the servo data preamble; generate a burst read
signal when the head passes over at least one of the slanted line
servo bursts; generate a position error signal (PES) in response to
a phase difference between the preamble read signal and the burst
read signal; and position the head in response to the PES.
2. The disk drive as recited in claim 1, wherein: the burst read
signal comprises a periodic signal; and a phase of the periodic
signal changes 180 degrees at the transition between the first
segment and the second segment.
3. The disk drive as recited in claim 1, wherein the servo data is
recorded on the disk by fabricating magnetic slants and
non-magnetic grooves.
4. The disk drive as recited in claim 3, wherein the first segment
and the second segment are formed by the slants.
5. The disk drive as recited in claim 1, wherein the servo data is
recorded on the disk by stamping a servo pattern on the disk using
a master stamping disk.
6. A method of writing servo data to define a plurality of servo
tracks on a disk of a disk drive comprising: recording a preamble;
and recording a plurality of slanted line servo bursts at a tilt
angle with respect to the preamble, wherein at least one of the
slanted line servo bursts comprises a first magnetic polarity along
a first segment of the slanted line and a second magnetic polarity
along a second segment of the slanted line.
7. The method as recited in claim 6, wherein: the burst read signal
comprises a periodic signal; and a phase of the periodic signal
changes 180 degrees at the transition between the first segment and
the second segment.
8. The method as recited in claim 6, wherein the servo data is
recorded on the disk by fabricating magnetic slants and
non-magnetic grooves.
9. The method as recited in claim 8, wherein the first segment and
the second segment are formed by the slants.
10. The method as recited in claim 6, wherein the servo data is
recorded on the disk by stamping a servo pattern on the disk using
a master stamping disk.
11. A disk for use in a disk drive, the disk comprising servo data
defining a plurality of servo tracks, the servo data comprising: a
preamble; and a plurality of slanted line servo bursts recorded at
a tilt angle with respect to the preamble, wherein at least one of
the slanted line servo bursts comprises a first magnetic polarity
along a first segment of the slanted line and a second magnetic
polarity along a second segment of the slanted line.
12. The disk as recited in claim 11, wherein: the burst read signal
comprises a periodic signal; and a phase of the periodic signal
changes 180 degrees at the transition between the first segment and
the second segment.
13. The disk as recited in claim 11, wherein the servo data is
recorded on the disk by fabricating magnetic slants and
non-magnetic grooves.
14. The disk as recited in claim 13, wherein the first segment and
the second segment are formed by the slants.
15. The disk as recited in claim 11, wherein the servo data is
recorded on the disk by stamping a servo pattern on the disk using
a master stamping disk.
Description
BACKGROUND
Disk drives comprise a disk and a head connected to a distal end of
an actuator arm which is rotated about a pivot by a voice coil
motor (VCM) to position the head radially over the disk. The disk
comprises a plurality of radially spaced, concentric tracks for
recording user data sectors and servo sectors. The servo sectors
comprise head positioning information (e.g., a track address and
servo bursts) which is read by the head and processed by a servo
control system to control the velocity of the actuator arm as it
seeks from track to track.
Various patterns have been employed to record the servo bursts in
the servo sectors, such as a quadrature (A,B,C,D) servo pattern
comprising squared bursts of transitions each recorded at a precise
interval and offset from a servo track centerline. A position error
signal (PES) is generated by demodulating and comparing the
amplitude of each servo burst (A,B,C,D) relative to one another.
Another known servo pattern comprises slanted line servo bursts
recorded at a tilt angle with respect to the preamble of the servo
sector. The PES is generated by comparing a phase difference
between the preamble signal and the burst signal generated as the
head passes over the slanted lines.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A shows a disk drive according to an embodiment of the
present invention comprising a disk having servo data defining a
plurality of servo tracks.
FIG. 1B shows an embodiment of the present invention wherein the
servo data comprises a preamble having a length that varies across
the radius of the disk, and a plurality of slanted line servo
bursts having a tilt angle that varies across the radius of the
disk.
FIG. 2 shows an embodiment of the present invention wherein the
disk comprises zoned servo data sectors.
FIG. 3A shows an embodiment of the present invention wherein the
slanted line servo bursts comprise a track pitch twice the track
pitch of the servo tracks.
FIG. 3B shows equations for defining the tilt angle and burst width
relative to the burst length and the track pitch of the slanted
line servo bursts.
FIGS. 4A-4B show an embodiment of the present invention wherein at
least one of the slanted line servo bursts comprises a first
polarity along a first segment of the slanted line and a second
polarity along a second segment of the slanted line.
FIGS. 5A-5B show an embodiment of the present invention wherein the
slanted line servo bursts comprises a first plurality of slanted
line servo bursts and a second plurality of slanted line servo
bursts, and the second plurality of slanted line servo bursts are
offset radially from the first plurality of slanted line servo
bursts.
FIG. 6 shows an embodiment of the present invention wherein the
servo data is printed on the disk using any suitable servo pattern
printing technique.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
FIG. 1A shows a disk drive according to an embodiment of the
present invention comprising a disk 2 including servo data recorded
in servo sectors 4.sub.0-4.sub.N defining a plurality of servo
tracks 6. FIG. 1B shows an example format of the servo data
recorded in servo sector 4.sub.3 as comprising a preamble 8 having
a varying length across the radius of the disk 2, and a plurality
of slanted line servo bursts 10 recorded at a tilt angle with
respect to the preamble 8. The tilt angle .alpha. varies across the
radius of the disk 2 commensurate with the varying length of the
preamble 8. The disk drive further comprises a head 12 actuated
radially over the disk 2 for generating a read signal 14, and
control circuitry 16 operable to position the head 12 over the disk
by processing the preamble 8 and slanted line servo bursts 10. A
preamble read signal is generated when the head 12 passes over the
preamble 8, and a burst read signal is generated when the head 12
passes over at least one of the slanted line servo bursts 10. A
position error signal (PES) is generated in response to a phase
difference between the preamble read signal and the burst read
signal, wherein the PES is used to position the head 12.
In the embodiment of FIG. 1B, the servo data in a servo sector
further comprises a sync mark 18 for storing a special pattern used
to symbol synchronize to a track address field 20. The track
address field 20 stores a track address in a suitable format (e.g.,
a Gray code) which is used to position the head over a target data
track during a seek operation. The control circuitry 16 demodulates
the servo data in the servo sectors to generate the PES, and
filters the PES using a suitable compensation filter to generate a
control signal 22 applied to a voice coil motor (VCM) 24. The VCM
24 rotates an actuator arm 26 in order to move the head 12 in a
direction that reduces the PES.
In the embodiment of FIG. 1B, the servo data is recorded using a
discrete track recording (DTR) technique. With DTR, the surface of
the disk 2 is fabricated with lands and grooves, wherein the lands
comprise a suitable magnetic material and the grooves comprise a
suitable non-magnetic material. In the example of FIG. 1B, the
grooves are represented by the shaded areas and the lands are
represented as the non-shaded areas. The magnetic material in the
lands is magnetized (e.g., DC erased) to have a predetermined
polarity. As the head 12 passes over the lands and grooves pulses
are induced in the read signal 14 representing the recorded data.
In the embodiment shown in FIG. 1B, the digital data in a servo
sector (e.g., the sync mark and track address) modulate the
fabrication process such that a "0" bit is recorded as a land and a
"1" bit is recorded as a groove. In an alternative embodiment, a
"0" bit may be recorded as land followed by a groove, and a "1" bit
may be recorded as a groove followed by a land.
In the embodiment of FIG. 1B, the slanted line servo bursts 10 are
recorded as interleaved segments of lands and grooves such that the
head 12 generates a periodic servo burst read signal having a
frequency related to the frequency of the preamble read signal. As
the head 12 deviates radially relative to the servo tracks, a PES
is generated in response to a phase offset .theta. between the
preamble read signal and the servo burst read signal as shown in
FIG. 1B. The phase offset .theta. may be generated in any suitable
manner, such as by computing a Discrete Time Fourier Transform
(DTFT) or a trigonometric function of the preamble read signal and
the servo burst read signal. The relationship between the phase
offset .theta. and the PES depends on the relationship between the
frequency of the preamble read signal and the frequency of the
servo burst read signal. The frequency of the preamble read signal
depends on the frequency of the transitions recorded in the
preamble field 8 (e.g., a 2T preamble), and the frequency of the
servo burst read signal depends on the geometry of the slanted line
servo bursts 10, including the tilt angle .alpha. as well as the
track pitch.
In one embodiment, the servo sectors 4.sub.0-4.sub.N are recorded
on the disk such that when the disk 2 is rotated at a constant
angular velocity, the servo data comprises a constant data rate
across the disk radius. Since the inner diameter of the disk 2 will
rotate slower than the outer diameter of the disk 2, the length of
the preamble 8 will decrease toward the inner diameter of the disk
2 as illustrated in FIG. 1B. In one embodiment, the tilt angle
.alpha. of the slanted line servo bursts 10 varies across the
radius of the disk commensurate with the varying length of the
preamble 8. In the example shown in FIG. 1B, the tilt angle
.alpha.1 at a first (outer) diameter of the disk is greater than
the tilt angle .alpha.2 at a second (inner) diameter of the disk.
Varying the tilt angle .alpha. across the radius of the disk 2
simplifies computing the PES by maintaining a substantially
constant relationship between the frequency of the preamble read
signal and the frequency of the servo burst read signal.
In the embodiment of FIG. 1A, the servo sectors 4.sub.0-4.sub.N are
recorded so as to generate a constant data rate across the entire
radius of the disk. This results in a single servo wedge format
from an outer diameter of the disk toward the inner diameter of the
disk. In an alternative format shown in FIG. 2, the servo sectors
are recorded in servo zones (e.g., Z0, Z1, Z2) wherein the data
rate is increased toward the outer diameter of the disk to achieve
a more constant linear bit density. In the zoned servo sector
embodiment, the servo sectors form servo wedges within each servo
zone such that the preamble length and tilt angle of the slanted
line servo bursts vary across each servo zone.
The slanted line servo bursts 10 may be recorded at any suitable
track pitch. In the embodiment of FIG. 1B, the slanted line servo
bursts 10 are recorded at a track pitch equal to the servo track
pitch (the track pitch of the track addresses). In an embodiment
shown in FIG. 3A, the slanted line servo bursts 10 are recorded at
a track pitch twice the servo track pitch. Selecting a larger track
pitch for the slanted line servo bursts 10 may improve the quality
of the read signal by immersing more of the head 12 in the lands
and the grooves. In one embodiment, the track pitch of the slanted
line servo bursts 10 remains constant over the disk radius, and in
an alternative embodiment, the track pitch of the slanted line
servo bursts varies over the radius of the disk. In the embodiment
where the track pitch varies, the equation for computing the PES in
response to the phase difference is adjusted accordingly.
In one embodiment, a desired burst track pitch (BTP) and a desired
burst length (BL) is selected for the slanted line servo bursts 10
based on suitable design criteria, such as signal quality, servo
sector density, and track pitch of the data tracks. Once the BTP
and BL are selected, the tilt angle .alpha. and the burst width
(BW) for the slanted lines may be computed based on the equations
shown in FIG. 3B. The burst length (BL) corresponds to the physical
length of a slanted line servo burst along the circumferential
direction of the disk over one cycle of the resulting servo burst
read signal. In the embodiment of FIG. 3A, the total length of a
slanted line servo burst equals one BL, whereas in the embodiment
of FIG. 1B the total length of a slanted line servo burst equals
two BLs. Increasing the total length of the slanted line servo
bursts 10 improves the accuracy of the measured phase, but reduces
the overall format efficiency by using disk area that could
otherwise be used to record user data.
The process of recording the slanted line servo bursts 10 on the
disk may result in an asymmetrical read signal. For example, with
DTR the read signal generated from reading the lands may be
asymmetrical compared to the read signal generated from reading the
grooves. In an embodiment shown in FIG. 4A, this asymmetry is
compensated by recording at least one of the slanted line servo
bursts with a first polarity along a first segment of the slanted
line and a second polarity along a second segment of the slanted
line. As illustrated in FIG. 4A, a phase of the periodic signal
when reading the slanted line servo bursts changes 180 degrees at
the transition between the first segment and the second segment
which helps compensate for asymmetry. Any suitable polarity
configuration may be employed in the embodiments of the present
invention, such as the polarity configuration shown in FIG. 4B.
In one embodiment, the phase of the servo burst read signal is
generated over multiple timing windows corresponding to the
polarity of each segment. In the embodiment of FIG. 4A, the phase
of the servo burst read signal may be generated over the "+"
segment, and then added to the phase generated over the "-" segment
offset by 180 degrees. In addition, the phase of the servo burst
read signal may be generated over more than the two cycles shown in
FIG. 4A by selecting a suitable geometry for the slanted line servo
bursts (e.g., selecting a suitable burst length (BL) and/or burst
track pitch (BTP) and/or tilt angle (.alpha.)). Increasing the
number of cycles to generate the phase of the servo burst signal
may improve the asymmetry compensation.
FIG. 5A illustrates another embodiment of the present invention
wherein the slanted line servo bursts comprises a first plurality
of slanted line servo bursts A and a second plurality of slanted
line servo bursts B, wherein the second plurality of slanted line
servo bursts B are offset radially from the first plurality of
slanted line servo bursts A. In the embodiment of FIG. 5A, the
second plurality of slanted line servo bursts B are offset by a
half track pitch of the slanted line servo bursts. This embodiment
may help compensate for distortions in the PES that can occur at
certain head offsets. In one embodiment, a phase measurement is
generated for each set of slanted line servo bursts A and B, and
the phase measurement corresponding to the highest SNR selected to
compute the PES. In another embodiment, the phase measurement
generated for both sets of slanted line servo bursts A and B are
combined with an 180 degree offset, and the resulting combined
phase used to generate the PES.
FIG. 5B shows an embodiment of the present invention which combines
the aspect of FIG. 4A with the aspect of FIG. 5A such that each set
of slanted line servo bursts comprises two or more segments of
opposite polarity. In the example of FIG. 5B, the first set of
slanted line servo bursts comprise an A segment and an A' segment
of opposite polarity, and the second set of slanted line servo
bursts comprise a B segment and a B' segment of opposite polarity.
As the head passes over the slanted line servo bursts, the read
signal comprises a pattern of the form A,A',B,B'. However, the
slanted line servo bursts may be recorded in any suitable manner to
achieve any suitable sequence of servo burst read signals, such as
A,B,A',B'.
In FIGS. 4A-5B the burst track pitch (BTP) equals the track pitch
of the servo tracks. However, any suitable BTP may be selected for
the embodiments shown in FIGS. 4A-5B, such as a BTP that is twice
the track pitch of the servo tracks as shown in the embodiment of
FIG. 3A.
Any suitable technique may be employed to record the servo data in
the servo sectors, such as the above described DTR technique.
Another known technique is referred to as "servo pattern printing"
(SPP) wherein the disk is fabricated with a magnetic material
across the entire surface and initialized to a desired polarity (DC
erased). A master stamping disk is created having the desired
magnetic pattern which is "stamped" onto one of the DC erased disks
to thereby magnetically print the servo data onto the disk. An
example embodiment of using SPP to record the servo data is shown
in FIG. 6 wherein the shaded areas of the digital data is
magnetized by the master stamping disk to have an opposite polarity
of the non-shaded areas. The slanted line servo bursts are formed
in a similar manner by DC erasing the slanted lines to a first
polarity (e.g., "+"), and then master stamping the disk to record
an opposite polarity (e.g., "-") to form the desired slanted line
pattern such as shown in FIG. 6.
Although not illustrated in the figures, in other embodiments of
the present invention the servo patterns may comprise suitable
gaps, such as a gap between the Gray coded track address 20 and the
slanted line servo bursts 10 of FIG. 1B, as well as a gap following
the slanted line servo bursts 10.
Any suitable control circuitry may be employed to implement the
flow diagrams in the embodiments of the present invention, such as
any suitable integrated circuit or circuits. For example, the
control circuitry may be implemented within a read channel
integrated circuit, or in a component separate from the read
channel, such as a disk controller, or certain steps described
above may be performed by a read channel and others by a disk
controller. In one embodiment, the read channel and disk controller
are implemented as separate integrated circuits, and in an
alternative embodiment they are fabricated into a single integrated
circuit or system on a chip (SOC). In addition, the control
circuitry may include a suitable preamp circuit implemented as a
separate integrated circuit, integrated into the read channel or
disk controller circuit, or integrated into an SOC.
In one embodiment, the control circuitry comprises a microprocessor
executing instructions, the instructions being operable to cause
the microprocessor to perform the steps of the flow diagrams
described herein. The instructions may be stored in any
computer-readable medium. In one embodiment, they may be stored on
a non-volatile semiconductor memory external to the microprocessor,
or integrated with the microprocessor in a SOC. In another
embodiment, the instructions are stored on the disk and read into a
volatile semiconductor memory when the disk drive is powered on. In
yet another embodiment, the control circuitry comprises suitable
logic circuitry, such as state machine circuitry.
* * * * *